Hand-held battery-operated devices, such as electric tooth brushes, radio transceivers, otoscopes, ophthalmoscopes, and cellular telephones, are well known in the art.
For such devices, battery operation is often both more convenient and safer than operating from standard alternating current (AC) outlets. Devices equipped with rechargeable batteries are yet even more convenient, because the batteries do not have to be replaced periodically.
One well known technique for recharging such batteries is to equip the hand-held device with an electrical connector. A recharger, which typically converts the high voltage AC available from an outlet to low voltage AC or direct current (DC), is coupled electrically to this connector. Devices that employ this approach are disclosed in U.S. Pat. Nos. 4,827,551 and 4,827,552. This technique has four well-known disadvantages. First, it requires a hole for the connector through the device's enclosure, making it difficult to seal the device's internal parts against water, dirt, solvents, and so forth. Second, the device, its battery or the charger can be discharged, damaged or destroyed if the terminals of the connectors are shorted, such as by water. Third, it provides an unlikely but still possible electrical connection between the user of the hand-held device and the AC outlet. Fourth, the electrical contacts may become dirty or corroded, making electrical connection difficult.
An improved charger, known in the art, eliminates any electrical connection between the hand-held device and the AC outlet. Instead, the required recharging power is coupled magnetically between the recharger and the hand-held device. The charger contains the primary of a transformer, and the hand-held device contains the secondary of a transformer. The primary and the secondary of the transformer are mechanically separable. When the two are placed in proper orientation and close proximity, a varying magnetic field is electrically induced in the primary of the transformer, and is then coupled to the secondary of the transformer. The secondary coil of the transformer is used to generate charging current for the rechargeable batteries. This approach allows the hand-held device to be completely sealed, and provides no electrical connection between an AC outlet and the hand-held device.
One device that employs such a charging arrangement is the Interplak.RTM. Home Plaque Removal Instrument manufactured by Bausch & Lomb of Tucker, Ga., and described, in part, in the disclosure of U.S. Pat. No. 4,845,795.
However, such an approach can produce substantial low-and medium-frequency magnetic fields in the vicinity of the charger.
Although at present there are no widely-accepted limits on human exposure to magnetic fields, most authorities recommend prudent avoidance.
An improved charger which reduces the magnetic fields produced in the vicinity of such a charger while maintaining the advantages of a separable core transformer is disclosed in the co-pending U.S. patent application Ser. No. 08/309,945 which is a continuation-in-part of U.S. patent application Ser. No. 08/269,392, now abandoned.
During charging with that technology, the stray magnetic fields are substantially reduced by forming a closed magnetic circuit between a charger base unit and the portable device. However, even in such improved chargers, significant magnetic fields may be produced by the charger when the hand-held device is removed from the charger.
When the hand-held device is placed in the charger, smaller magnetic fields may still be produced by such improved chargers. Such smaller magnetic fields continue to be produced unnecessarily even when the batteries in the hand-held device are fully charged.
It is an object of the present invention to retain the advantages of a mechanically-separable transformer charger arrangement for hand-held rechargeable-battery operated devices, while substantially reducing the exposure to low- and medium-frequency magnetic fields produced near such a charger arrangement by turning off or otherwise disabling the charger either at times when such a hand-held device is removed from the charger, or at times when the batteries in such a hand-held device are fully charged, or both.
It is a further object of this invention to reduce the power consumption of such chargers either at times when such a hand-held device is removed from the charger, or at times when the batteries in such a hand-held device are fully charged, or both.